=For a true shock wave, the medium is disturbed. For instance, with a
=sonic boom there is a region of compressed air, but no region of
=rarefied air (as there is in a normal sound wave). Thus, as the boom
=passes through the air, each little chunk of air ends up displaced from
=its initial position. Although the pressure, average velocity, etc. of
=the air is the same afterwards as before, the position of each chunk
=has changed, and hence it's average velocity (during passage of the
=boom) was non-zero.
=--
=--James McLean
=jmclean@chem.ucsd.edu
=post doc
=UC San Diego, Chemistry
Been a long time since I studied shocks, so I can't provide a lot of detail. As
I write this, I am referring to "Astrophysical Formulae" by K. R. Lang.
Pressure, velocity, and temperature do change across a shock front. I think a
shock is, by definition, a discontinuity. The changes are described by a set of
"jump conditions" called the Rankine-Hugoniot equations. Each equation can be
expressed in terms of the adiabatic gas constant (gamma) and M1, the Mach number
for the gas behind the shock front. The equations are derived directly from
Euler's equation, energy conservation, and the ideal gas law. If subscript 2
represents gas ahead of the shock and subscript 1 the gas behind the shock, the
jump conditions are: